Vehicle leader-follower systems are used in various military and transportation applications in which one vehicle, called the “leader”, moves along the ground, in the air, or space, and one or more other vehicles, each called a “follower”, are to follow the leader and/or move along laterally displaced from the leader.
A leader-follower system approach known in the art is one in which the follower follows closely behind or spaced from the leader, such as less than one second from the leader. In current close leader-follower systems, the follower is too slow to respond to changes in speed and bearing of the leader. The follower must first observe or be communicated the change in speed and bearing of the leader before providing inputs to its controls to adjust its own trajectory in order to stay at the proper offset distance from the leader. Thus, there is an inherent delay between the leader changing its speed and/or bearing and the follower changing its speed and/or bearing. This inherent delay causes poor performance in maintaining the same path as the leader and the proper follow distance unless the follow distance is greater than the leader speed multiplied by the sensing and communications delay time.
FIGS. 1A and 1B show operation of a conventional close leader-follower system. At Time=0, the follower is directly behind the leader and at the desired follow distance. At this time, the leader is providing input to its control system to decrease speed and turn right. At time Time=T0 (some time interval later), the follower finally is made aware of the change in speed and bearing of the leader, but the follower is already off its path and too close to the leader. Meanwhile, the leader is providing different input to its control systems that is currently unknown to the follower.
In ground vehicles and air vehicles, the time for the vehicle to react to an input change is generally on the order of a one second or more. This reaction time provides for a lower limit on the follow distance using a conventional leader-follower approach. Limiting the follow time interval to two seconds or more is unattractive for many applications because this sets the maximum follow distance to be as much as 80 feet at 30 MPH, for example, and 160 feet at 60 MPH. For certain leader-follower applications, such large follow distances are not acceptable.
Thus, a leader-follower system and method is needed that can allow relatively close following of a leader vehicle without sacrificing vehicle speeds.